Abstract: The results of studies on plant breeding and biosystematics showed that P. tomentosa originated in hybrid. Taxonomists have made a classification of various varieties of P. tomentosa but couldn't get unified opinion.The genetic variation of 105 clones collected from 15 regions of 6 provinces in main distribution area of P. tomentosa was analysed by means of polyarclamid gel electrophoresis. 8 types of isoperoxidase pattern were obtained from them, which showed genetic polymorphism within P. tomentosa.The clones, which showed the characteristics of type 1, occupied 85.7% of the total. Their distribution areas coincide with the distribution areas of P. tomentosa. The clones which belong to type 1, type 3, or type 4 ppossess different morphology, phenology, growing habits, sex and distribution. They were nominated as new varieties in some books. The differentiation of isoperoxidase is eailier than differentiation of morphology,so using these differences to supplement morphological taxonomy can make complicated things simpler.In order to further analyse the relationships among the 8 types of isoperoxidase patterns, we adopted their SCIP. When similarity distance (similarity coefficents + similarity distance=1) is 0.23, the varieties of type 1 to type 4 can be grouped into one. They should be the major type of P. tomentosa. The varieties of type 5 to type 8 have distant relationships with P. tomentosa and they possibly occurred in modern times. Because P. tomentosa is self originated in hybrid, its mordern population should be the hybrid population derived from the crossing of P. tomentosa with many other species of sect. Leuce repeatedly.